1. Technical Field
The present invention relates to a surface acoustic wave chip formed with an inter-digital transducer that performs conversion between electric signals and surface acoustic waves, a surface acoustic wave device, and a manufacturing method for implementing the device.
2. Related Art
In electronic and communications components such as mobile phones and television receivers, surface acoustic wave devices (hereinafter, referred to as “SAW devices”) serve as a resonator, band-pass filter, or the like. In such SAW devices, connections are established through wire bonding or bumping with components housed in the package, e.g., a surface acoustic chip, and a circuit board.
FIGS. 27A and 27B are diagrams showing an example of a known SAW device. Specifically, FIG. 27A is a cross sectional view of the SAW device, and FIG. 27B is a cross sectional view along a line A-A of FIG. 27A. For details of such a SAW device, refer to Patent Document 1 (JP-A-2003-1.10391).
In the drawings, a SAW device 1 is configured so that a pair of inter-digital transducers or comb electrodes (hereinafter, referred to as IDTS) 3 are formed entirely over a piezoelectric substrate 2 that is made of crystal or the like, and are sealed with a cover 9 via a cavity 4. Here, the cover 9 is a glass substrate.
As shown in FIG. 27B, the IDTs 3 each include a terminal 5 on the piezoelectric substrate 2, and as shown in FIG. 27A, a connection is established with an external electrode 8 using a conductive through hole 7.
For attachment of the cover 9 to the piezoelectric substrate 2, an electrode pattern 6 is formed to the edge portions of the piezoelectric substrate 2 along its rim.
With a configuration such, through anode attachment, the glass cover 9 is securely sealed against the piezoelectric substrate 2 at its rim edge portions.
Another example of a previously-known SAW device takes a configuration such as shown in FIG. 28, which shows the simplified manufacturing process of FIG. 2 of Patent Document 2 (JP-A-8-213874), for example.
To be more specific, in FIG. 28, a reference numeral 1 denotes a wafer made of a piezoelectric material such as crystal. As shown in the drawing, from one piece of wafer 1, a plurality of surface acoustic wave chips 2 are simultaneously formed for use in forming surface acoustic devices.
Each surface acoustic wave chip 2 is formed with inter-digital transducers or comb electrodes (IDT electrodes) 3a and 3b that are entirely over a substrate configured by the wafer 1. The IDT electrodes 3a and 3b are made of an aluminum pattern or the like. The surface acoustic wave device seals therein the surface acoustic wave chips 2 with a glass substrate serving as a cover (not shown).
As shown in FIG. 28, the wafer 1 is entirely formed with a metallic layer 5, e.g., an aluminum layer, and thereon, the surface acoustic wave chips 2 are formed by photolithography or the like. That is, the IDT electrodes 3a and 3b provided to the surface acoustic wave chip 2 are formed so as to oppose each other so that their electrode fingers dig into each other.
FIGS. 29A and 29B both show still another example of a previously-known SAW device, which is shown in FIG. 4 of Patent Document 3 (JP-A-2001-94388), for example. Specifically, FIG. 29A is a cross sectional view of the SAW device in the longitudinal direction, and FIG. 29B is an enlarged view of select portions of FIG. 29A. The SAW device has a configuration such that an aluminum extractor electrode 80 is formed on a piezoelectric substrate 32. The piezoelectric substrate 32 also carries thereon an inter-digital transducer (IDT), a reflector (not shown), or the like. An aperture section 81 carries therein a conductive embedding member 82, and is heated in a vacuum so that a connection is established between the extractor electrode 80 and an external electrode 83, thereby attempting to suppress the effects of connection resistance due to alumina occurring on the surface of the extractor electrode 80. In view thereof, unlike the invention, there are no characteristics in the configuration of an IDT or the like.
In the previously-known configuration of FIGS. 27A and 27B, the terminal 5 of the IDT 3 is provided on the piezoelectric substrate 2, and for electric insulation from the terminal 5, the electrode pattern 6 is provided for attachment at a position away therefrom on the plane.
As a first problem, the piezoelectric substrate 2 is required to be large relative to the size of the IDT 3. This impairs space efficiency, resultantly causing a difficulty of downsizing the SAW device 1.
With the previously-known manufacturing method of FIG. 28, in the process of electrode formation, in the IDTs provided in a pair, there needs to be a no-electrode-layer portion 4 formed around the IDT electrodes 3a and 3b to make them separate from each other.
The IDT electrodes 3a and 3b are each preferably formed with an oxidation layer on their surfaces for protection purpose mainly due to the necessity of preventing the risk of a short circuit therebetween. When the IDT electrodes 3a and 3b are of aluminum electrodes, in view of production efficiency, it is considered preferable that every IDT electrode is formed with a protection layer on the surface through anode attachment over the wafer 1.
As a second problem, as shown in FIG. 28, it is difficult to form such a protection layer all at once over the surface of every IDT electrode due to the configuration wherein the IDT electrodes 3a and 3b are provided so as to be away from each other on the wafer 1.